Conventionally, a biometric authentication technology has been used that uses personal biometric information such as hand veins, a fingerprint, an iris, a face or the like, as an authentication method of a person who is entering or leaving a room, a facility or the like, without human intervention. Authentication using biometric information has an advantage over authentication using a magnetic card or a personal identification number (PIN) in that it does not need to care about loss, forgetfulness, and fraudulent use.
Taking an example where veins are used as biometric information, a general biometric authentication technology will be described. Basic steps of the vein authentication apparatus are as follows. First, the vein authentication apparatus irradiates near-infrared light on a part of a human body, such as a palm, where an image of veins can be easily captured, and extracts the image of veins by capturing strength distribution of reflected or transmitted light.
The vein authentication apparatus stores images of veins of individuals that have registered beforehand. Registered biometric information is also called “registration data” or “registration template”. The vein authentication apparatus verifies a registration template with an obtained image of veins (called “verification data”) that is captured on authentication to determine whether the two images are equivalent.
However, biometric information for the same person may fluctuate to a certain extent. Therefore, when determining the equivalence of the images of veins, fluctuation needs to be allowed to a certain extent. Typically, the vein authentication apparatus first executes positioning of the two, represents the likeness between the two by a measure called similarity, and if the similarity is greater than a threshold, determines that a person in question is one of the registered individuals.
Positioning is executed, for example, to increase a degree of the equivalence between the registration data and the verification data as much as possible, by virtually moving one of them. Here, “virtually moving” means converting the coordinate system representing an image of veins.
A registration template is usually stored in an IC card owned by a user or a storage device (database) of a server. Positioning and a calculation process of the similarity are executed by a computer located close to a user or a server under centralized management.
As a conventional technology to further improve authentication precision, a method is known that uses other information obtained together with biometric information for authentication. Such information is called “auxiliary information” below. Using auxiliary information, authentication precision can be improved with increased information, without additional imaging times at the expense of a user.
As a conventional technology that uses auxiliary information, there is a technology that extracts finger veins and finger profiles from a captured image, and executes positioning of finger directions by the finger profiles (see, for example, Patent Document 1). Also, there is a technology that detects the position and the direction of a hand, and if they are inappropriate, indicates that to the user (see, for example, Patent Document 2), or guides the user so that biometric information can be captured with an appropriate position (see, for example, Patent Document 3).
Also, there is a technology that selects the best shot of a face among moving images (see, for example, Patent Document 4).